Circuit Design

The inductor coil is one of the fundamental electronic componentshowever it is very less used in the electronic circuits as compared to the other components. The reasons are mainly due to its physical size, sensitivity to the presence of electromagnetic field, unavailability of wide range of inductance values etc. The inductors cannot be included in the Integrated Circuit Chips due to its three dimensional geometry and size. Hence most of the circuit designers try to avoid inductor coils from their circuits and prefer ‘Synthetic Inductor Circuits’ which simulates an inductor using other electronic components. This article discusses on the design of a Synthetic Inductor circuit and demonstrates its working on a sample application circuit. The Synthetic Inductor can be easily made using a capacitor, Op-amp, a resistor and a variable resistor using which the inductance value can be varied by a large range. When using SMD components the entire circuit will take less space than the actual inductor.

In an audio play back device, the entire audio signals are separated into different bands and applied to the corresponding type of loudspeaker. The Tweeters are normally fed with frequencies above 5 kHz, Mid-range speakers are fed with frequencies in the range of 300 Hz to 5 kHz, and Sub-Woofers with 300 Hz to 40 Hz and Woofers are fed with frequencies below 40 Hz. Since the musical sound normally falls around the maximum frequency of 5 to 8 KHz, Tweeters are not so common in audio devices. For driving the Mid-range Speakers a high pass filter of cut-in frequency around 300 Hz is enough and for Woofers a Low pass filter with cut-off frequency around 40 Hz will suffice. Bass-beats of the songs appear in the Sub-Woofer range and a Band-pass filter can be used to separate out these frequencies from the entire audio signals. This project discusses the design and implementation of a Multiple Feed Back (MFB) Band pass filter for Sub-Woofer frequencies.

The entire audible voice spectrum stretches from around 20Hz to 20 KHz and there is not loudspeaker design which can reproduce all these frequencies with the same effect. The Woofers are made to produce subsonic sounds (below 20 Hz) and there are musical instruments which can produce frequencies above 18 KHz. To reproduce all these sounds different types of loudspeakers are fed with their own band of frequencies extracted from the music.The filter circuits that are used at the output side of the audio device which filters out different band of frequencies and use them to drive different type of loudspeakers are called Audio Crossover Circuits. Three-way cross over circuits are very common in output side of the audio devices which filters out frequency bands for Tweeters, Mid-range Speakers and Sub-Woofers. This tutorial discusses the design and implementation of Two-way audio cross-over circuit using Active filters for quality filtering.

This article discusses about the design of a simple audio mixer circuit. An op-amp based summing amplifier is used here to mix two sounds. The audio mixing is demonstrated with the help of mixing a high frequency musical sound with a low frequency bass beat, where the musical sound is generated by a musical IC and the bass beat played at a mobile phone and is captured and amplified through a microphone and amplifier circuits. The different sounds in songs like the sound of the guitar, drums, the voice of the singer etc. are recorded as separate tracks using separate microphones. More than 10 numbers of tracks are very common in normal quality songs. How is such a circuit assembled? What are the major precautions and restrictions when using this circuit? Keep on reading this tutorial to find more interesting information about electronics of audio mixing. 

The Pulse Position Modulation (PPM) is a modulation technique designed to achieve the goals like simple transmitter and receiver circuitry, noise performance, constant bandwidth and the power efficiency and constant transmitter power. In Pulse Position Modulation the amplitude of the pulse is kept constant as in the case of the FM and PWM to avoid noise interference. Unlike the PWM the pulse width is kept constant to achieve constant transmitter power. The modulation is done by varying the position of the pulse from the mean position according to the variations in the amplitude of the modulating signal. This article discusses the technique of generating a PPM wave corresponding to a modulating sine wave. The Pulse Position Modulation (PPM) can be actually easily generated from a PWM waveform which has been modulated according to the input signal waveform.  

The amplifiers are devices which produces an output signal which is several times higher in amplitude than the input signals. The ratio of the amplitude of the output signal from an amplifier circuit to the amplitude of the input signal is called Gain. The amplifier circuits are normally designed for a fixed amount of gain. There are amplifiers with very low gain, like the amplifiers at the loudspeaker side of an audio device and also there are amplifiers with very high gain, like the amplifiers in the radio receivers or amplifiers at the microphone side of an audio device. The Automatic Gain Control (AGC) amplifiers are another category of amplifiers which can vary its gain according to the input signal level. They provide enough amplification for the weak signals and prevent strong signals from getting over amplified.  

A burst power when used other than the continuous power can save the total power supplied to an inertial load while achieving the same performance from the device. The performance can be varied by varying the width of the pulses. This is the technique called Pulse Width Modulation (PWM) which is in use since a long time for controlling motor speed and other similar inertial machineries. The PWM technique is use in devices like DC motors, Loudspeakers, Class -D Amplifiers, SMPS etc. They are also used in communication field as-well. The modulation techniques like AM, FM are widely used RF communication whereas the PWM is modulation technique is mostly used in Optical Fiber Communication (OFC).The PWM in a communication link greatly saves the transmitter power. The immunity of the PWM transmission against the inter-symbol interference is another advantage. This article discusses the technique of demodulating a PWM wave. 

The Pulse Position Modulation (PPM) is a modulation technique designed to achieve the goals like simple transmitter and receiver circuitry, noise performance, constant bandwidth and the power efficiency and constant transmitter power. In Pulse Position Modulation the amplitude of the pulse is kept constant as in the case of the FM and PWM to avoid noise interference. Unlike the PWM the pulse width is kept constant to achieve constant transmitter power. The modulation is done by varying the position of the pulse from the mean position according to the variations in the amplitude of the modulating signal.The Pulse Position Modulation (PPM) can be actually easily generated from a PWM waveform which has been modulated according to the input signal waveform. The PPM can be demodulated both synchronously and asynchronously. The synchronous demodulation is complex as it requires synchronization of the receiver with the transmitter.  

This article discusses about a simple circuit that can reproduce the sound signals captured through a microphone on a loudspeaker. The microphone is a device which is used to capture sound signals and forms an essential part of most of the electronic gadgets. The microphone converts the sound signals in the environment to their corresponding electrical signals. These electrical signals are actually very small in amplitude and they need to be amplified several hundred times before it could be reproduced through a loudspeaker.  This circuit is made with the help of two stage transistor amplifier and a op-amp based loudspeaker driver amplifier. To demonstrate its working, music is played in a mobile phone which is kept near the microphone and the same music with more loudness is generated at the loudspeaker connected to the circuit. Continue reading to find out how the circuit is assembled and how it works. 

This article discusses how to design a simplest active bass separator circuit with design details. This is basically a low pass circuit which is used to separate out low frequency sounds from audio signals at audio play back devices. A simple loudspeaker is not capable of reproducing all the frequencies of the audible range. Different kinds of loudspeaker are available which can reproduce the sound at certain range of frequencies. The bass separator circuit alone is realized with the help of commonly available op-amp ICs. For demonstrating the working a bass beat is played in a mobile phone which is captured, amplified and mixed with a high frequency musical signal and is then again separated out using the bass separator circuit and reproduced in a loudspeaker. Read more to find out how the circuit is assembled and how it is tested and used.  

The PWM is a technique which is used to drive the inertial loads since a very long time.The simple example of an inertial load is a motor. Apply the power to a motor for a very short period of time and then turn off the power: it can be observed that the motor is still running even after the power has been cut off from it. This is due to the inertia of the motor and the significance of this factor is that the continuous power is not required for that kind of devices to operate.  

There are different kinds of modulation technique based on varying the properties of a pulse train. The Pulse Width Modulation (PWM) varies the width of individual pulses according to the amplitude of the modulating signal. The Pulse Position Modulation (PPM) varies the position of individual pulses from their mean position according to the amplitude of the modulating signal. The PWM is a kind of modulation technique indented for power efficiency, but the power required to transmit individual pulses varies significantly.

Most of the electronic devices work on a single positive power supply except few like op-amps, oscillators etc. Majority of the amplifiers circuits or amplifiers ICs are also works on positive power supply. Such kind of devices can operate only with input signals having only positive voltages. Devices like amplifiers, modulators, demodulators etc. are supposed to work with natural signals as input. Since the natural signals like sine wave, audio signals etc. has both positive and negative cycles they have to be modified in such a way the single supply electronic circuits can operate them. Clamping is the common technique that is applied on the input signals to modify them so that the circuits can process the entire signal without losing either positive or negative half. In this method the entire waveform is shifted to positive of negative voltage side hence making them single polarity varying voltage.  

The electronic circuits like amplifiers, modulators etc. have a particular range at which they can accept the input signals. Any signals which have amplitude higher than this particular rage can cause distortion in the output of the circuit or may even cause damage to the circuit components itself. Since most of the devices works on single positive supply the input range will also be in the positive side. Since the natural signals like sine wave, audio signals etc. has both positive and negative cycles and varying amplitude they have to be modified in such a way the single supply electronic circuits can operate them. Clipping of a wave is the common technique that is applied on the input signals to modify them so that they fall in the operating range of the circuits. This article discusses the details of the clipping and the practical positive and negative clipping circuits.  

Explained here is an interesting circuit designing tutorial about impedance measurement of a speaker.  In speakers, impedance measurement forms a crucial part as it is always needed to get the perfect every time. From small earphones to the large bass woofers, one cannot expect sound to be too lousy or too sharp even at normal levels.  It, hence, becomes the responsibility of the circuit design to get the perfect sound delivered to our ears.  Interestingly, impedance variance is quite a common feature in speakers depending on their application. A telephone and a home theater system speaker would have totally different requirements in terms of impedance measurement. This circuit designing tutorial on impedance measurement describes basics with sounds, frequency and impedance. Further, a thorough detail regarding practical impedance measurement has been explained.  Explore all the technical details and find out how you can make yourself a master piece of a speaker through this impedance measurement process. 

The simple pulse modulation technique called Pulse Amplitude Modulation (PAM) proved to be more power efficient than the PWM and consumes constant power for individual pulses like PPM. In PAM the amplitude of the individual pulses are varied according to the amplitude of the modulating signals. The PAM modulator and demodulator circuits simple compared to other kind of modulation and demodulation techniques. There are two kinds of PAM one in which the pulses have the same polarity and the other in which the pulses can have both positive and negative polarity according to the amplitude of the modulating signal.The PAM modulation technique is widely used in high speed digital communications like telephone modems, Ethernet etc. They are used to drive LED lights more efficiently than using PWM method. Unlike the PPM the transmitter and receiver synchronization is not required for the PAM. 

 The FM demodulator is done with the help of a circuit called Phase Locked Loop (PLL). A PLL should have basic functional blocks like Voltage Controlled Oscillator (VCO), Phase comparator, Low Pass Filter (LPF) and Source follower. In the demodulator circuit the VCO generates a frequency which matches the original carrier frequency and compares the phase of that with received FM wave using the Phase comparator. The output of the Phase comparator is filtered out using the LPF and is current amplified using a Source follower.The output of the source follower matches the original message signal. To implement all the above mentioned circuitry is a difficult task, but there are ICs available which has all these circuit blocks embedded in it. In this article the FM demodulation is done with the help of a PLL IC called HEF4046. 

This tutorial explains circuit designing using a 555timer to generate a frequency modulated wave. Along with 555 IC timers, the circuit is designed around a Wien Bridge Oscillator circuit and a clamping circuit. Out of many methods of frequency generation, this tutorial covers one of the simplest and most efficient circuits. From its generation to modulation, the wave suffers minimal distortion and hence, a near accurate output is generated. The circuit can be easily assembled on a breadboard and connectors can be clamped anywhere to get an output on CRO. The process is divided into three states, namely, sine wave generation; positive wave clamping; and wave modulation. The wave is generated using Wien Bridge oscillator, is clamped and then is modulated by 555 based timer circuit. There are several curious questions to this design, such as in what mode is the 555 timer made to work? How the Wien Bridge Oscillator circuit is designed?  Continue reading to reveal these answers and other interesting information about this circuit. 

The amplitude modulation is the simplest modulation technique among the wide verity of modulation techniques in use. In this technique the amplitude of a high frequency signal is varied corresponding to the variation in the amplitude of the low frequency modulating signal. The demodulation of an AM wave can be done with only few components and unlike most of the demodulation technique there is no synchronization required between the modulator and demodulator circuits. The message signal appears as an envelope over the amplitude of the carrier wave and the demodulator make use of this to extract the modulating signal from the carrier and hence the technique of AM modulation is called envelope detection.This article demonstrates how to generate an Amplitude Modulation (AM) and demodulate the same wave to get the original modulating wave. The AM wave is generated based on the circuits explained in article on AM modulation. 

The AM modulation is a kind of modulation technique which is in use since the very early days of wireless data transmission.  In a radio transmission system there is a relation between the ranges of frequencies which can be transmitted wirelessly with the length of the transmitting antenna. The relation is inversely proportional to one another, means as the frequency of the signal to be transmitted increases the length of the antenna can be reduced and as the frequency of the signal to be transmitted decreases the length of the transmitting antenna should be increased accordingly.Using an antenna of few meters the frequencies in the range of Mhz can be easily transmitted to a distance. The basic purpose of the wireless transmitting system in early days was to transmit the audio signals, but to transmit audio signals which fall in the range of few Khz an antenna of more than a kilometer height would have been required.